1. Field of the Invention
The present invention relates to a clamp having an arm for clamping a workpiece. The arm is rotatable at a predetermined angle by a drive mechanism.
2. Description of the Related Art
Clamp cylinders have conventionally been used in order to clamp a component of an automobile or the like to be welded. Such a clamp cylinder is disclosed in U.S. Pat. No. 4,458,889, for example.
As shown in FIGS. 16 and 17, in the clamp cylinder disclosed in the U.S. Pat. No. 4,458,889, a piston rod 2 is actuated by a cylinder 1c to reciprocate between a pair of divided bodies 1a, 1b. A coupling 3 is connected to an end of the piston rod 2. A pair of links 5a, 5b and a pair of rollers 6a, 6b are rotatably installed to both ends of the coupling 3 respectively by a first shaft 4. An arm 8 which is rotatable at a predetermined angle is connected between the pair of links 5a, 5b by a second shaft 7.
In this case, the pair of rollers 6a, 6b are slidable by a plurality of needles 9a which are installed to holes. The rollers 6a, 6b are slidable along track grooves 9b defined on the bodies 1a, 1b. The piston rod 2 is guided by the rollers 6a, 6b and displaceable together with the rollers 6a, 6b. 
However, in the above conventional clamp cylinder disclosed in the U.S. Pat. No. 4,458,889, a surface of a workpiece (not shown) may be damaged when clamped by the arm 8 since the rotating arm strikes against the workpiece.
Specifically, when a door with its outer surface coated is clamped by the arm 8, an end (clamping portion) of the rotating arm 8 may strike by inertial force (rotational force) against the outer surface of the door, thereby causing damages on the coated surface.
It is a general object of the present invention to provide a clamp which makes it possible to reduce inertial force (rotational force) of an arm of the clamp when a workpiece is clamped thereby, for protecting the surface of the workpiece from an impact exerted by the arm.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.